Phosphorylation and Dephosphorylation of Neurofilament Proteins in Retinal Ganglion Cell Neurons In Vivo

Abstract

The cytoskeleton of most higher eukaryotic cells is composed of three filamentous systems, which serve varying dynamic and structural roles in cellular function. Two of these systems, the 80 Å microfilaments and the 230 Å microtubules, are composed of subunit proteins that are phylogenetically highly conserved. By contrast, the 100 Å intermediate filaments are encoded by a large multigene family, the members of which are differentially expressed in different tissues (Fuchs and Hanukoglu, 1983). On the basis of biochemical and immunological criteria, five major classes of intermediate filaments have been defined (Lazarides, 1980). These include keratin filaments, found in cells of epithelial origin; desmin filaments, predominantly found in smooth, skeletal and cardiac muscle cells; vimentin filaments, present in cells of mesenchymal origin; glial filaments, constituents of certain glial cell types; and neurofilaments, present in many differentiated neurons of vertebrates and invertebrates. This classification emphasizes the tissue specificity of intermediate filaments, although it is now known that subunits from more than one class may coexist in some tissues at certain developmental stages (Osborn et al., 1980; Drager, 1983).